Process Engineering Equipment Handbook 2009 Part 2 pdf

It is almost universally agreed that stainless steel is the most cost-effective long- term solution for construction of the air-inlet system. The premium between stainless steel over painted carbon steel can now be as low as 20%, whereas there are no further painting costs and the life is infinitely longer. The grade of stainless steel is also important. It is recognized that the lower grades, such as American Iron and Steel Institute AISI 304 and AISI 321, do not have sufficient corrosion protection, particularly if the material is work hardened. AISI 316 is the most popular choice since it has up to 18.5% chromium, a metal whose presence helps to build up a passive protective film of oxide and prevents corrosion. Together with 10 to 14% nickel content, the steel has an austenitic structure that is very ductile and easily welded. It also can have a low carbon content (below 0.03%) as well as a molybdenum content of between 2.0 and 3%, which increases its resistance against pitting. Indeed, one operator has paid a significant premium in both cost and delivery time by insisting that the molybdenum content be no lower than 2.5%. Not only are the filter housings now constructed in AISI 316 but also almost all of the items such as vane separators, door locks, hinges, and instrumentation are supplied in this same material. These inlet systems will give a long life, and they look good as well. A typical system is shown in Figs. A-64 and A-65. A-62 Air Filtration; Air Inlet Filtration for Gas Turbines FIG. A-49 Drain valve. (Source: Altair Filters International Limited.) The attention to detail is now evident. Figure A-65 clearly shows the elaborate drain systems that are now installed. In addition, the stainless-steel housings are carefully segregated in the manufacturing shop to prevent any cross-contamination from any other ferrous materials, which includes tooling. Figure A-66 shows a Brunei 4 platform where five of the engines had been retrofitted with this system. In summary the main requirements of a filtration system in a tropical environment are 1. Protection against tropical rainstorms by vane separators 2. The inclusion of an integrated drain system 3. The selection of AISI 316 stainless steel as the material of construction 4. Protection against droplet carryover by a final stage vane separator Air Filtration; Air Inlet Filtration for Gas Turbines A-63 FIG. A-50 Salt penetration through filters. (Source: Altair Filters International Limited.) A-64 Air Filtration; Air Inlet Filtration for Gas Turbines FIG. A-51 Salt penetration through filters. (Source: Altair Filters International Limited.) FIG. A-52 Corrosion at silencer outlet. (Source: Altair Filters International Limited.) Air Filtration; Air Inlet Filtration for Gas Turbines A-65 FIG. A-53 Water penetration through the inlet silencer. (Source: Altair Filters International Limited.) FIG. A-54 Corrosion in plenum. (Source: Altair Filters International Limited.) 5. Protection against insects with an insect screen 6. The use of dust extract systems only where essential The Offshore Environment* In Europe in the late 1960s, the only data generally available on the marine environment was generated from that found on ships. Since at that time there was considerable interest in using gas turbines as warship propulsion systems, several attempts were made to define the environment at sea, with particular respect to warships. A-66 Air Filtration; Air Inlet Filtration for Gas Turbines FIG. A-55 A detached plenum lining. (Source: Altair Filters International Limited.) *Source: Altair Filters International Limited, UK. Adapted with permission. Air Filtration; Air Inlet Filtration for Gas Turbines A-67 FIG. A-56 A corroded inertia filter. (Source: Altair Filters International Limited.) FIG. A-57 A corroded weather louvre. (Source: Altair Filters International Limited.) A-68 Air Filtration; Air Inlet Filtration for Gas Turbines FIG. A-58 Corrosion downstream of filters. (Source: Altair Filters International Limited.) FIG. A-59 Corrosion downstream of filters. (Source: Altair Filters International Limited.) Not only was it found difficult to produce consistent data, but other factors such as ship speed, hull design, and height above water level had major effects. It became apparent that predicting salt in air levels was as difficult as predicting weather itself. Since the gas turbine manufacturers had defined a total limit of the amount of the contaminants that the turbines could tolerate, some definition of the environment was essential to design filter systems that could meet these limits. Many papers and conferences were held with little agreement, as can be seen in Fig. A-67. However since the gas turbine industry is a conservative one, it adopted the most pessimistic values as its standard, namely the National Gas Turbine Establishment (NGTE) 30-knot aerosol (Table A-11). It was treated more as a test standard rather than what its name implied. In the absence of any other data, this was used to define the environment on offshore platforms, despite the fact that they were much higher out of the water, and did not move around at 40 knots! This then defined the salt in air concentration, but did not address any other particulates. In hindsight, it now seems naive that the offshore environments were originally considered to be clean with no other significant problems than salt. Many Air Filtration; Air Inlet Filtration for Gas Turbines A-69 FIG. A-60 Corrosion debris in inlet duct. (Source: Altair Filters International Limited.) equipment specifications were written at that time saying the environment was “dust free.” In the early 1970s there was also a lively debate as to whether the salt in the air was wet or dry. One argument was put forward that if the salt was wet it would A-70 Air Filtration; Air Inlet Filtration for Gas Turbines FIG. A-61 A paint blister. (Source: Altair Filters International Limited.) FIG. A-62 A new filter housing awaiting installation. (Source: Altair Filters International Limited.) [...]... FIG A- 62 (Source: Altair Filters International Limited.) FIG A-64 A stainless-steel filter housing (Source: Altair Filters International Limited.) A- 72 Air Filtration; Air Inlet Filtration for Gas Turbines FIG A-65 A stainless-steel filter housing (Source: Altair Filters International Limited.) TABLE A-11 Microns NGTE 30-knot Aerosol Salt Content, ppm 13 0.0038 0. 021 2 0.1404... fuel consumption Particles of 2 mm and less are generally the major cause of fouling Smoke, oil mist, and sea salt are common examples The particles are attracted to the metal surfaces by a variety of forces, including impaction, electrostatic, and capillary action The composition of the particle, again, is important in determining the rate of fouling In marine environments, dry dust particles are often... protect against fouling ᭿ To prevent particle fusion ᭿ To protect against corrosion Erosion Erosion is caused by particles impacting and wearing away the metal surfaces The high speeds of the rotating blades collide with the airborne particles and produce a quite large change in energy, which results in fragments of metal being blasted out of the blade surface Even particles as small as 10 mm in diameter... it tended to transfer large particles of debris into other areas of the turbine, causing even more problems There was also a view put forward that it accelerated hot end corrosion Modern cleaning methods use a detergent sprayed into the engine on a cold cycle, leaving it to soak and then washing it off with clean water Particle fusion Dry particles, which range in size from 2 to 10 mm, could, on old... that over a 12- month period, 700 tons of grit blast had been used! The Problems Encountered In general, problems were slow to appear, typically taking three to five years after start-up, but since a lot of equipment had been installed at about the same time, the problems manifested themselves like an epidemic These problems could be categorized as follows: 1 Erosion of compressor blading 2 Short intervals... chloride) is the main offender In the cold parts of the engine it is the sodium chloride that does the damage, whereas in the hot parts of the engine it is sodium sulfate (or sulfidization) that creates most of the corrosion Sodium sulfate is produced from the combination of sulfur in the fuel and sodium chloride in the air It is important to recognize that the corrosion process is self-propagating, and, once... quality of the inlet air over a period of one month This showed the modified installation to be 10–14 times more effective, in terms of particle penetration It is not surprising that Shell has now retrofitted 78 installations worldwide In total this design has been selected for 21 2 new and retrofitted gas turbine engines Filter systems that were an operational irritation every 15 days or so are now forgotten... 45-mm H2O means lower fuel consumption, higher output, and longer filter life for operators High-efficiency filtration This feature has been aerodynamically designed to ensure that maximum particulate efficiency is achieved with the minimum resistance to airflow The * Note: Trademarks are specific to the source for this section Each manufacturer will have its own equivalent terms and trademarks A- 82 Air... of dust and process types and its ability to capture all particles, not only those that can be charged electrically (as in ESPs) (See Fig A-80.) Another reason for the recent success of fabric filters is that they operate by passing the dust-laden gas through a dust cake that is constantly being built up with the support of the fabric This enables the removal of a large portion of the finest particles,... A- 82. ) The Optipulse® cleaning concept (Optipulse is a trademark for a proprietary design of this information source.) Pulse-jet fabric filters operate with dust-laden gas approaching the filter elements from the outside, depositing the particles on the fibers of a depth-filtering medium The clean gas leaves the open end of the filter element, which is typically of tubular design with a diameter of 120 –150 . Limited.) TABLE A-11 NGTE 30-knot Aerosol Microns Salt Content, ppm < ;2 0.0038 2 4 0. 021 2 4–6 0.1404 6–8 0.3060 8–10 0.4 320 10–13 0.6480 >13 2. 0486 Total 3.6000 require a further stage of vane separators. an increase in fuel consumption. Particles of 2 mm and less are generally the major cause of fouling. Smoke, oil mist, and sea salt are common examples. The particles are attracted to the metal. cycle, leaving it to soak and then washing it off with clean water. Particle fusion Dry particles, which range in size from 2 to 10 mm, could, on old engine designs, pass through the engine causing